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Dielectric barrier discharges (DBDs) have been used for ozone production since the 19th century. Beyond their historic application, their versatility extends to diverse fields, including plasma medicine and material surface modification. DBDs most commonly operate in the filamentary regime, characterized by short-lived microdischarges (often called filaments) igniting randomly in the inter-electrode space, which can cause inhomogeneities in surface treatment or film deposition. Although this makes them generally undesirable for such applications, filaments hold significant potential as micro-reactors for localized treatment or deposition if their ignition mechanism and chemistry can be understood and controlled. While considerable work exists on understanding DBD regimes and avoiding the filamentary mode, poor reporting has been made on deposition processes at the filament scale. In this thesis, we aimed to address this with a system of immobilized DBD filaments. The latter was achieved through local gap reduction via dielectric patterning. This approach facilitated local discharge analysis and allowed us to test the potential of these filaments for surface patterning applications. For this last point, propargyl methacrylate (PMA) was chosen as test-case precursor for thin film deposition. The study of the discharge focused on the dynamics and properties of individual filaments and of the overall discharge under varying operating parameters such as gap width, applied voltage, PMA feed rate, and dielectric pattern geometry. For this purpose, we performed high-speed camera imaging, electrical measurements, and optical emission spectroscopy (OES) imaging of a filament. Deposition with the immobilized filaments system from Ar/PMA mixture resulted in patterned coatings. The higher reactivity inside the filaments generated circular hill-like areas (spots), while a thinner film was also deposited between the spots. Spatially resolved characterizations using profilometry, X, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

Plasma technology is very modular and can operate in moderate conditions. Additionally, it activates gas molecules by high energy electrons instead of heat, and it can convert intermittent renewable electricity into value added chemicals. Last but not least, the possibility of integrating plasma with a catalyst in “plasma catalysis” enables the selective production of desired products and can lead to improvements in the process efficiency. Therefore, in the past few years, plasma technology has started to be considered as a green alternative for fossil-based gas conversion processes. However, the industrialization of this process faces several challenges, such as the need for better insight in plasma-catalyst interactions, high energy consumption, as well as challenges for the development of industrial scale efficient reactors. In the framework of this thesis, we have tried to add to the state-of-the-art in plasma-based nitrogen fixation, by dealing with these three challenges, using a combined experimental and modelling work., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

Nitrogen is an essential component of all living organisms and a basic element for synthesizing many chemical products. However, N2 is chemically inert and inaccessible to most organisms in its original form. Therefore, it must be first converted into other more reactive forms like ammonia or nitrates in a process named “Nitrogen Fixation”. Nitrogen fixation (NF) with low energy consumption and minimal CO2 emissions is a significant challenge in today's technological landscape. The natural processes allowing NF are mostly lightning and the activity of some bacteria. The global population growth also increases food demands, thus the industrialization of agriculture using nitrogen-based fertilizers has driven the development of artificial NF processes. In the beginning of the 20th century, intensive research efforts led to the development of several industrial NF processes. The most developed processes are (I) Birkeland–Eyde (B-E) process, (II) Frank–Carlo (F-C) process, and (III) Haber–Bosch (H-B) process. As a result of high energy consumption, the first two processes were abandoned and quickly replaced by the H-B process. In the H-B process, nitrogen from air is combined with hydrogen during steam methane reforming under extremely high pressures (100−250 bar) and moderately high temperatures (500°C) in presence of an active catalyst (Fe or Ru–based catalysts) to yield a high proportion of ammonia. For a fully optimized and integrated H-B process, an energy efficiency as low as 0.48 MJ/mol of nitrogen is reported. Nevertheless, despite its effectiveness, this process consumes almost 1%–2% of the world’s total energy resources and emits more than 180 million tons of CO2 annually. In addition, a fully operational H-B process demands a large infrastructure that does not allow for decentralization on a small scale which makes the transportation requirement an additional disadvantage of this method. It is therefore necessary to develop a new NF process allowing for lower en, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

Plasma treatment of polypropylene (PP) is a well-established method of improving its surface properties. However, the efficiencies of different plasma discharges are seldom compared. Herein, we discuss the differences in PP treated by three arc-based commercial plasma jets working in dry air, Plasmatreat rotating plasma jet (PT-RPJ), AFS PlasmaJet & REG; (AFS-PJ), and SurfaceTreat gliding arc jet (ST-GA), and by the low-temperature RF plasma slit jet (RF-PSJ) working in argon. The AFS-PJ has a significantly different reactive species composition dominated by nitrogen oxides. It induced higher thermal loads leading to surface damage. The other arc-based jets (PT-RPJ and ST-GA) created the PP surface with higher oxygen and nitrogen concentration than the low-temperature RF-PSJ. It induced a higher adhesion strength measured on PP-aluminum joints.

Objective: This study evaluates the application of a plasma discharge for the decontamination and removal of bacterial biofilms in small-diameter polytetrafluoroethylene (PTFE) tubes. The latter simulates the environments of an endoscope working channel., info:eu-repo/semantics/nonPublished

L’azote est l'élément le plus abondant dans l’atmosphère terrestre, composée de 78% de N2. C’est également un élément essentiel pour de nombreuses molécules biologiques, comme la chlorophylle ou les protéines. Cependant, la triple liaison liant les deux atomes d’azote est une des plus stables, ce qui rend l’absorption directe d’azote atmosphérique par la plupart des organismes impossible. Il peut malgré tout être fixé par des procédés industriels, mais ceux-ci produisent plus de 3% des émissions totales de CO2 et consomment environ 2% de l’énergie totale produite mondialement. Il est donc nécessaire, dans le contexte actuel de réchauffement climatique et de crise énergétique, de trouver des alternatives plus écologiques.Dans le cadre de cette thèse, la fixation de l’azote par plasma atmosphérique en présence d'eau est étudiée. Pour cela, un microplasma est initié à la surface d’une solution aqueuse afin de fixer l’azote directement en solution. Ce procédé profite des quantités presque illimitées de N2 et de O2 présents dans l’atmosphère, et en outre, pourrait être alimenté par une source d’énergie verte. Dans le cadre de la thèse, nous avons déterminé les mécanismes de formation, en phase gazeuse et aqueuse de l’azote fixé en solution, que ce soit sous forme réduite ou oxydée. Le rendement énergétique a également été évalué. Enfin, les solutions traitées par plasma sont ensuite utilisées dans un cas concret, afin d’étudier leur effet sur la croissance de plantes. La phase gazeuse a été analysée par spectrométrie d'émission optique (OES), spectrométrie infrarouge à transformé de Fourier (FTIR) et un senseur électrochimique industriel, Testo 350. La phase aqueuse est analysée par chromatographie ionique, spectroscopie UV-visible et des mesures de pH.Dans la première partie, nous montrons le rôle prépondérant du mécanisme de Zeldovich non-thermique pour la formation, dans un premier temps, d’oxyde d’azote (NO) en phase gazeuse. Le NO est ensuite oxydé, que ce soit en p, Nitrogen is the most abundant element in Earth's atmosphere, which represents about 78% in the form of N2. It's an essential component for many biomolecules, such as chlorophyll or proteins. However, the triple bond located between both nitrogen atoms, is one of the strongest bonds in chemistry, and renders molecular nitrogen inaccessible to most organisms. Despite this fact, the Haber-Bosch/Ostwald processes are able to fix nitrogen into nitrates or ammonia. Those processes are well optimized but account for more than 3% of the global O2 emission and consume about 2% of the worldwide energy production. With global warming and the energetic crisis, it's essential to find a sustainable way to fix nitrogen.In this thesis, the nitrogen fixation by an atmospheric DC microplasma, in the presence of water, is studied. An atmospheric pressure microplasma is ignited at the water surface to fix the nitrogen directly into the solution. The process takes advantages of the unlimited quantities of N2 and O2 in the atmosphere and we green energy can be used to produce and maintain the discharge. In this work, we determined the mechanisms of nitrogen fixation in the gas and liquid phase, into the oxidized or reduced form. The energy cost is also evaluated. Finally, the solutions are used for the growth of plants. To analyze the gas phase, OES, FTIR and an industrial electrochemical sensor, Testo 350 are used. Ionic chromatography, UV-visible spectrometry and pH measurements are used for the liquid phase.In the first chapter, the importance of the non-thermal Zeldovich mechanism is highlighted for dissociation and the oxidation of N2 in NO in the gas phase. For further oxidation, the role of the H2O2 is discussed. The influence of the polarity of the microplasma is also studied on the mechanisms and yield. When the water is the cathode, the amount of nitrates form is higher and nitrates are the only species of interest detected by ionic chromatography.In the second chapter, the dis, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

Cold atmospheric plasmas are a known source of reactive species enabling various treatments, from the healing of chronic wounds to the treatment of surface cancers. Therapeutic endoscopic procedures require developing specific flexible tools that can be used through or alongside endoscopes. Plasma devices for endoscopy have aroused significant research interest over the past few decades, but their electrical behaviour is not yet fully understood and predictable. There is thus a clear need for a robust model that provides a way to understand and optimize future devices. In this work, for the first time, an electrical equivalent model of a long plasma source (comprising plasma generation, transport and target interaction) was designed, implemented, and validated. System parameters were estimated based on the system geometry and independent measurements. The model reliably reproduces the double ignition (in the quartz chamber and at the treatment site) observed experimentally. Simulations globally agree with measurements taken for various gas gap distances and input voltages. Internal parameters that are difficult to measure, such as the electrical charge at the gas gaps, were inferred. The model can predict leakage current in the body and current at the target site. This work provides a new understanding of endoscopic plasma systems that could be used in the future to ensure patient and operator safety., SCOPUS: ar.j, info:eu-repo/semantics/published

info:eu-repo/semantics/published